This invention relates to optical spectroscopy, and in particular to the purging of attachments or accessories designed for use with optical spectrometers.
By purging is meant the introduction and flushing with a suitable atmosphere of the optical path sections of a spectrometer or its attachment for the purpose of minimizing or eliminating the ambient atmosphere that would otherwise be present. This is done to remove extraneous spectral artifacts from sample spectra and to enhance energy throughout. Purge atmosphere is meant to include any gas or any combination of gases which have satisfactory optical properties in the wavelength range of interest. Although purging is especially useful for single beam instruments in the mid-infrared region of the spectrum, where sample and background spectra are taken independently and where ambient atmospheric carbon dioxide and water interfere, this invention is meant to apply to the purging of attachments used in all optical spectrometers, regardless of spectrometer design or wavelength range. Suitable atmospheres are nitrogen, argon, helium, or hydrogen gas. The purge atmosphere is typically supplied at a pressure slightly above ambient pressure, so that it tends to displace the ambient air in the region of interest. Seals are generally provided to seal off the purged region from the ambient atmosphere but the seals are relatively primitive since any leakage which will occur at the seals is from the higher pressure purged region to the ambient, and thus causes little harm.
Conventional commercially available spectrometers generally provide a purge facility in several different ways. An enclosure can be provided over the sample compartment into which open entrance and exit beam ports for the optical beam. These ports are also used to supply purge gas to the sample compartment. When the spectrometer interior is purged, so will the enclosed sampling compartment be purged.
An alternative is to provide a transparent window that seals off a port in the spectrometer wall, through which the beam can enter and exit for use with external accessories, in which case a purge port can be provided in the spectrometer wall to which a tube can be connected at one end. The opposite tube end would be connected to the accessory which would mimic the sample compartment of the spectrometer.
The problem most often encountered with the conventional system is the time delay as a result of, for example, changing samples within the attachment located within the enclosed sample compartment. This requires breaking the seal to access the sample thus allowing ambient atmosphere into the system. It typically takes 20 minutes to re-purge the instrument. Hence, 20 minutes are wasted each time a new sample is to be analyzed.
With the external accessory in the conventional design, again the system seal is broken when sample changes or other adjustments become necessary, resulting in the same unavoidable delay while the system is re-purging.